This invention relates in general to measuring air flow. In particular, this invention relates to systems and methods for measuring air flow at multiple points of an air channel.
A critical step in the process of manufacturing integrated circuits from a silicon wafer is coating the silicon wafer with a uniform layer of photoresist. Typically, the photoresist is applied to the wafer by a machine known as a spin coater. A spin coater may stand alone, or it may be included in a track system with other devices that perform tasks such as baking the wafer and developing the photoresist.
In a typical application, the spin coater includes a dispenser that deposits the photoresist onto the substrate (i.e., the wafer) and a substrate support (e.g., a circular platter) that rotates while holding the substrate to cause the photoresist to spread out over the surface of the substrate. The spin coater also includes a high efficiency particulate air (HEPA) filter, and the spin coater directs filtered air from the HEPA filter towards the wafer to help disperse the photoresist. The space separating the HEPA filter and the wafer is known as the air channel.
In order to obtain a uniform thickness of photoresist on the wafer, it is important for the air flow in the air channel to be uniform across the wafer. For example, if the air flow has greater velocity at the center portion of the wafer than at intermediate or edge portions, the spin coater is likely to leave a thinner coating of photoresist at the center. Accordingly, manufacturers of spin coaters typically publish guidelines which specify acceptable air velocity measurements for the spin coaters. For example, guidelines may specify that air flow velocity for a particular application should be between 4.95 and 5.05 feet per second at six different points in a cross section of the air channel, with the cross section located two inches above the substrate support.
Consequently, integrated circuit manufacturers periodically measure air flow velocities in spin-coater air channels to determine whether the air flows conform to the required guidelines. If the air flow for a spin coater is out of specification, corrective actions are taken. For example, the HEPA air filter may be cleaned or replaced, or a service technician may be called in to repair or adjust other parts of the spin coater.
In a conventional facility for manufacturing integrated circuits, the operator of the spin coater uses a hand-held anemometer to take the required air-flow readings. However, as recognized by the present invention, there are numerous disadvantages associated with this practice. Among those disadvantage is that readings taken with a hand-held anemometer typically are not sufficiently accurate. For example, inaccurate readings may be caused by holding the operative end of the anemometer slightly out of position in the air channel, tilting the anemometer so that its longitudinal axis is not perpendicular to the air channel, and/or rolling the anemometer (i.e., rotating the anemometer about its longitudinal axis) so that the opening in its operative end is not properly aligned with the air channel.
Therefore, as recognized by the present invention, a need exists for more reliable devices and methods for measuring air flow in air channels such as those used in spin coaters.
One aspect of the invention is a metering plate for measuring air flow at multiple points in an air channel. The metering plate includes a body that has multiple passages through the body. The body is adapted to be positioned across the air channel in an orientation that places two or more of the multiple passages at two or more respective locations within the air channel. The body is also adapted to receive two or more flow meters at the two or more passages, respectively. In addition, the body is configured so that respective air flow velocities at the two or more locations when the body is positioned across the air channel substantially matches air flow velocities at the two or more locations when the body is not positioned across the air channel. Accordingly, the metering plate can be used to measure the air flow velocities at the two or more locations without substantially altering the air flow velocities at the two or more locations.
In an example embodiment, the body includes two or more holders dimensioned to secure the two or more flow meters to the body with respect to pitch and roll. Consequently, different sets of measurements made with the device at different times accurately reflect differences in air flow at the different times.
An advantage of a metering plate according to the invention is that it can be used to obtain highly accurate readings from different machines. Similarly, such a metering plate can be used to obtain highly accurate readings from the same machine at different times. Consequently, the invention makes it possible to reliably compare air flow readings from the same machine over time and to reliably compare air flow readings from different machines. The invention thus provides advantages to manufacturers and users of machines like spin coaters, which have air channels and precise requirements for the air flow within the air channels. For example, the present invention helps integrated circuit manufacturers keep spin coaters functioning properly, which increases manufacturing efficiency and product quality.